Fracturing method

ABSTRACT

An improved method of fracturing an underground fluid bearing formation penetrated by a well bore for the production of fluids therefrom by injecting a composition comprising cement, sand and oil, capable of forming a fluid permeable barrier in said formation at a pressure sufficient to form fissures therein extending from said well bore, and thereafter maintaining pressure on the composition for a predetermined period to permit the composition to set and form a fluid permeable barrier in the formed fissures.

United States Patent Harnsberger et a1.

[54] FRACTURING METHOD [72] Inventors: Bobby G. Harnsberger; Joy T.Payton,

both of Houston, Tex.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: June 19, 1970 [21] App1.No.: 47,879

[52] US. Cl ..166/281, 166/283 [51] Int. Cl ..E21b 33/138 [58] Field ofSearch ..166/276, 281, 283, 292-294; 106/90, 98

[56] References Cited UNITED STATES PATENTS 3,208,522 9/ 1965 Roebuck eta1 166/283 3,429,373 2/1969 Harnsberger et a1. ..166/276 2,805,7199/1957 Anderson 106/98 X 2,933,135 4/1960 Johnson ....166/283 X3,046,222 7/1962 Phansalkar et a1 ..166/283 3,145,774 8/1964 Patchen..106/98 X [151 3,654,991 [451 Apr. 11, 1972 3,368,623 2/1968 Carteretal..166/276 3,467,193 9/1969 Messenger ..166/294X OTHER PUBLICATIONS Oil-Well Cementing Practices in the United States, N.Y., Am. Pet. Inst.,1959, pp. 70- 72.

Primary Examiner-David H. Brown Attomey-Thomas H. Whaley, Carl 6. Reisand James F. Young [57] ABSTRACT 8 Claims, No Drawings FRACTURING METHODThe present invention relates to an improved method for the recovery ofpetroleum from an underground petroleum containing fonnation.

It is known to use various fluids in fracturing operations for theinitiation and/or enlargement of fissures in underground fluidcontaining formations such as a hydrocarbon bearing formation. In thisknown procedure, a fluid called the fracturing fluid is pumped into awell bore and forced out into the formation under a pressure sufficientto open up fissures in the formation and/or to enlarge any naturalfissures therein. It is desirable to add to the fracturing fluid apropping agent or mixture of such agents to maintain the created and/orenlarged fissures in the open position to enhance the flow of formationfluids therethrough into the well bore for subsequent recovery therefromby conventional recovery techniques. Among known propping agents aresolid particles such as sand, walnut shells, glass beads, metal pellets,plastics and the like.

Suitable fracturing fluids include fresh water, brines, gelled water(fresh or brine), gelled acids, and liquid hydrocarbons such asgasoline, kerosene, diesel oil, gas oil and the like, that usually haveincorporated therein a bodying or gelling agent such as sodiumpalmitate.

Among the disadvantages associated with the known hydraulic fracturingmethods using propping agents is the tendency of the formation afterbeing fractured to reseal itself at the induced or enlarged fissureswith the result that the propping agents are crushed or forced into theformation and their beneficial effects destroyed.

Another disadvantage is that the propping agents are removed from theirlocations in the fissures by the flow of formation fluids duringsubsequent petroleum production operations and their propping functionis materially decreased or lost with a resultant loss of production ofpetroleum fluids.

It has now been found that the above disadvantages can be overcome ormaterially lessened by the novel fracturing method of the presentinvention.

An object of the present invention is to provide an improved formationfracturing method.

It is known from our commonly assigned U.S. Pat. No. 3,429,373 to treatan unconsolidated sandy formation with a treating composition which setsand forms a permeable cement barrier. The formed permeable cementbarrier prevents the movement of unconsolidated sand particles with theflow of formation fluids during producing operations. The disclosure ofthis patent is herein incorporated by reference.

How these and other objects of the invention are accomplished willbecome apparent with reference to the accompanying disclosure. in atleast one embodiment of the practice of the invention, at least one ofthe foregoing objects will be achieved.

In accordance with the present invention the improved method comprisesfracturing an underground fluid bearing formation penetrated by a wellbore for the production of fluids therefrom by injecting a compositioncomprising cement, sand and oil which is capable of forming a fluidpermeable cement barrier in said formation at a pressure sufficient toform fissures therein extending from said well bore, and thereaftermaintaining pressure on said composition for a predetermined period topermit the composition to set and form said fluid permeable cementbarrier in the formed fissures.

The invention in a further aspect also comprises carrying out thefracturing operation with a fracturing fluid such as water, oil or thelike, which optionally may contain a propping agent such as sand, glassbeads or the like including mixtures thereof, and after the formationhas been fractured and optionally propped open, then injecting thecomposition into same to lock in the propping agent and/or to keep thefissures open by the formed fluid permeable barrier.

An unexpected advantage accruing from this embodiment of the inventionis that the placed propping agents are prevented from being washed outof the formed formation fissures bythe permeable cement barrier duringproduction of formation fluids with a resultant decrease and/orinterruption of production of the desirable formation fluids.

The method of the present invention is believed to be particularlyadaptable to fracturing operations wherein the underground formationsare composed of soft calcareous matter such as the Annona Chalkformations in Louisiana. The method of the present invention willprevent and/or retard the closing up or healing of the fissures in suchfractured calcareous fonnations.

The composition useful in the method of the present invention shouldmeet certain requirements.

The sand component of the composition should be of a U.S. Sieve Sizebetween about 12 and 40 mesh to permit a good cement to be formedtherewith and also to provide effective propping and/or to preventsealing of the fissures. A mesh size between about 20 and 40 mesh ispreferred for excellent interstitial permeability without sacrificingdesirable propping effects.

The sand component of the composition should be employed in an amount offour to eight parts by weight per part by weight of the cementcomponent. It has been found that a frac sand, i.e. one customarily usedin fracturing can also be used in the composition provided the mesh sizeis about 12 to about 40 mesh.

The use of a graded sand with the large grains being not more than abouttwice the diameter of the smaller grains, i.e. 12 mesh to 20 mesh, 20 to40 mesh is preferred, since premature bridging of the sand grains islikely to be avoided.

Sand particles coarser than 12 mesh and finer than 40 mesh areunsuitable for use in the treating composition of the invention. Thecoarser particles are unsatisfactory because the strength of the setsand-cement mixture is too low. Very fine sand particles also areunsuitable because the permeability of the set sand-cement mixture isundesirably low.

The cement component of the composition of the present invention shouldbe present in the dry mixture in a ratio of about one part of cement tofrom four to about eight parts by weight of sand on a weight basis. Thecement component of the composition of the present invention may be anyof the cements normally used in oil well cementing operations. it ispreferred that the cement component be a light weight Portland cementhaving a density of about 75 lbs. per cubic foot and a chemical analysisapproximately as follows: silicon dioxide 38.3%, aluminum oxide 13.0%,ferric oxide 5.2%, calcium oxide 35.7%, magnesium oxide 1.6% and sulfurtrioxide 2.4%, with a loss on ignition of approximately 3.3%. Thisparticular light weight Portland cement has been found to be mostsuitable in the composition of the present invention since permeablecements made from this cement are most stable against attack by theformation brines containing sodium chloride or sodium sulfate. Someother oil well cements are not as resistant to attack by formationbrines or sulfate solutions and therefore are not as practical for usein the cement composition of the present invention. These other cementsappear to lose some of their compressive strength and become eroded fromcontact with sodium chloride and sodium sulfate solutions. In contrast,the cements of the composition of the present invention are generallyvery resistant to erosion by sodium chloride or sodium sulfate solutionsand do not lose their compressive strength even after prolonged exposurethereto.

The hydrocarbon oil component of the composition should be employed inan amount of from about 0.4 part to about 0.8 part by weight per part byweight of cement. It is preferred that the oil component be employed inan amount of about 0.5 to about 0.6 part by weight per part by weight ofcement. Use of the oil component in this amount provides sufficient oilto wet the cement and sand components of the composition and at the sametime avoids an excess thereof which could possibly damage the formationwhen the composition is placed therein.

Suitable hydrocarbon oils include the kerosene and diesel oil fractionsof a petroleum crude oil as well as refined oils of high viscosity.

A necessary component of the petroleum oil fraction of the compositionof the present invention is an oil wetting water repellent agent, i.e.,a water insoluble oleophilic material of relatively high molecularweight which will permit the petroleum fraction to oil wet the surfacesof the sand and cement particles in the composition. The oil wettingagent must contain an oleophilic group and a polar group forpreferential adsorption on or at the oil and sand-cement interfaces.Representative oil wetting agents useful in the practice of the presentinvention include the relatively high molecularweight amines such as forexample, the C -C hydrocarbylamines, decyl-, dodecyland octadecylamine,the C -C fatty alcohols such as cetyl and octadecyl alcohol, the C -Calkylated phenols and naphthols, natural fatty materials such aslanolin, lard, cottonseed oil and fatty acid glycerides, amides such asthe C -C fatty acid amides, and mixtures of these oil wetting agents.

The oil wetting agent is used in an amount of from about 0.01 to about0.10 by weight, based on the weight of the cement particles in thecomposition.

It is preferred to incorporate a minor amount of finely divided silicain the composition to impart improved compressive strength to thehardened cement. This component is most effective when the fluidpermeable cement barrier in the formed fissures is likely to be subjectto attack by aqueous brine and/or sulfate solutions.

The finely ground silica component of the composition must be of a sizesufficient to pass through the openings of a No. 200-325 sieve (U.S.Sieve Series), i.e., (a sieve having openings of 00029-00017 inch). Thefinely divided silica component is used in an amount of from about 0.01to about 0.30 part, preferably 0.02-0.04 part, by weight per part ofcement.

When the composition contains the finely ground silica, this componentis added to the intimately mixed sand, cement, oil and oil wettingagent, then the resulting admixture is further mixed. A preferred mixingprocedure is to mix the sand and cement components, separately mix theoil and oil wetting agent, mix these two mixtures together, and finallyto add the finely divided silica thereto and further mix the resultingadmixture.

The composition can be suspended in the aqueous carrier medium in anamount of from about 1-10 pounds, preferably -10 pounds per gallon. Theaqueous carrier medium may also contain from about 1 to about percent byweight of sodium chloride, preferably about 8-12 percent.

The aqueous carrier medium containing the suspended oil wet sand andcement solids is pumped down the well bore and into the formation to befractured at a rate of from about 5 to 40 barrels of the suspendedsolids in the carrier medium per minute.

An aqueous surface active agent solution is preferably used to contactthe emplaced oil wetted sand-cement particles to displace the oiltherefrom and to initiate hardening of the cement. The surface activeagent used must be a water soluble material to penetrate theoil-sand-cement interface and water wet the cement particles and removethe oil therefrom. Representative surface active agents that willperform satisfactorily in the present invention include anionic,cationic and nonionic materials such as the alkyl, aryl or alkarylsulfates and sulfonates, the sulfated and sulfonated alkyloxyatedamides, esters or ethers, hydrocarbylamine salts, esters or ether-estersof natural fats and oils, or alkyl phenols. The surface active agentsinclude polyoxy-ethylene sorbitanmonolaurate, -monopalmitate and-monooleate, oxyalkylated amyl phenol, alkaryl polyether alcohols andpolyoxyethylene ether. A preferred surface active agent is anethoxylated nonylphenol containing about 9.5 moles of ethylene oxide,known by the trade name Surfonic N-95. The cement also can remain incontact with the cement particles for an extended time period.

In either case the formation is shut in for a time sufficient to pennitthe cement to harden.

The carrier medium containing the suspended solids is pumped down thewell bore and into the formation at rates which may vary with wellconditions. Generally a rate of from about 5 to 40 barrels of thesuspended solids in the carrier medium per minute is suitable toperforate an interval. Such rates should give the satisfactory resultsand the resulting permeable cement barrier formed in the formation has asufficiently high compressive strength and sufficient permeability topermit the flow of formation fluids therethrough.

In the practice of this invention for the fracturing of undergroundformations to increase their fluid productivity and/or permeability, afracturing fluid is placed in a well penetrating the formation to befractured, optionally through the tubing, adjacent and in contact withthe face of the formation to be fractured. If desired or required,packing is employed to isolate and confine the fracturing fluid to aportion of the well exposing the formation to be fractured. Pressure isthen applied via the fracturing fluid so as to build up the pressure onthe formation exposed to the fracturing fluid to a value great enough tocause the formation to be fractured and form fissures therein.

The pressure required to fracture the formation varies from place toplace depending upon the depth and/or the nature of the formation beingfractured. Suitable fracturing pressures are in the range l,000-l5,000p.s.i. and may be higher. When the formation fracturing pressure hasbeen reached, the formation is fractured and the formed fissures provideadditional areas for the drainage of formation fluids.

Following is a description by way of example of the method of thepresent invention.

EXAMPLE I A primary fracturing fluid is prepared by intimately mixingfive parts by weight of a frac sand having a particle size of 20 to 40mesh, one part by weight of a hydraulic cement known by the trade nameTrinity Lite Wate Cement and 0.033 part by weight of 200-325 mesh finelyground silica flour. There is added to the mixture with stirring 0.4part by weight of a petroleum oil fraction which also contains 5 percentby volume of an oil wetting agent such as dodecylamine.

The resulting composition of oil wet solids is suspended in an amount ofS-lO pounds per gallon of water, and is pumped down the bore hole to thefracturing site. Pressure is applied to the suspension to fracture theformation and create fissures therein. The suspension is also forcedinto the created fissures by the imposed pressure and optionally can beforced further into the formation to enlarge and/or extend them byincreasing and/or maintaining sufficient pressure thereon. In theformation fissures the oil wet sand-cement composition settles out ofthe carrier liquid. Thereafter the settled composition is preferablycontacted with a aqueous solution containing about 1 percent by weightof a water soluble surface active agent such as Surfonic N-95 topenetrate the oil-sand-cement particles and water wet the cement. Thecement hardens and forms a fluid permeable barrier in the fissures topermit formation fluids to pass therethrough while keeping the fissuresopen to the flow of these fluids.

EXAMPLE II In a tailing in operation, the formation is fractured in aconventional manner such as by hydraulic fracturing using a frac sand asthe propping agent in the aqueous fracturing fluid. After the formationis fractured, the composition suspended in the aqueous carrier is pumpeddown the well bore and is injected into the created fractures. Theinjected composition may then be treated with an aqueous solutioncontaining a water soluble surface active agent to contact the cementcombe caused to set by allowing the aqueous carrier medium to ponent andcause same to harden. The well is shut in until the cement has set andforms the fluid permeable barrier in the fissures. Thereafter, formationfluids can be removed through the fonned barrier.

We claim:

1. In a method of fracturing an underground fluid bearing formationpenetrated by a well bore for the production of hydrocarbons therefromemploying a fracturing fluid which is injected into the formation at apressure sufficient to form fissures therein extending from said wellbore and force the fracturing fluid into the formed fissures, theimprovement which comprises employing as the fracturing fluid acomposition consisting essentially of cement, from four to eight partsby weight of sand having a mesh size between about 12 and 40 mesh, from0.02 to 0.04 part by weight of a finely divided silica of 200-325 meshsize, from 0.4 to 0.8 part by weight of a hydrocarbon oil and from 0.01to about 0.10 part by weight of a water insoluble olephilic material ofrelatively high molecular weight, each per part by weight of cement,said composition being suspended in an aqueous carrier medium in anamount of from about 1 to pounds per gallon of said aqueous carriermedium, contacting said fracturing fluid in said fissures with anaqueous solution of a surface active agent to water-wet the cementparticles, maintaining said pressure on said contacted fracturing fluidfor a period sufiicient to permit the composition to set and form afluid permeable cement barrier in said fissures, and thereafterproducing hydrocarbons from said formation through said formed permeablecement barrier.

2. In a method as defined in claim 1, initially fracturing saidformation by a fracturing fluid containing a propping agent, andthereafter injecting said composition into the fissures formed by saidfracturing fluid.

3. In a method as defined in claim 1, wherein said fracturing occurs ina soft calcareous formation.

4. In a method as defined in claim 1, wherein said oil is a memberselected from the group consisting of kerosene, diesel oil and refinedoil.

5. A method of preventing the closure of fissures in a hydrocarbonbearing underground fractured soft calcareous formation to permit theproduction of hydrocarbons from said formation, which comprisesinjecting a hydraulic fracturing fluid down a bore hole communicatingwith said formation at a pressure sufficient to form fissures therein,injecting into said formed fissures a treating composition consistingessentially of cement, from four to eight parts by weight of 20-40 meshsize sand, from 0.4 to 0.8 part by weight of a hydrocarbon oil, from0.01 to 0.10 part by weight of a oil wetting agent, and 0.02 to 0.04part by weight of finely divided silica of 200325 mesh size, each perpart by weight of cement, said composition being suspended in an aqueouscarrier medium in an amount of from about 1 to 10 pounds per gallon ofsaid carrier medium, contacting said injected treating composition insaid fissures with an aqueous solution of a water soluble surface activeagent to water wet the cement component thereof, maintaining pressure onsaid composition for a predetermined period to permit the formation of afluid permeable cement barrier in said formed fissures, where saidhydrocarbons in said formation can be recovered through said formedpermeable cement barrier.

6. In a method as defined in claim 5, wherein said oil is a memberselected from the group consisting of kerosene, diesel oil and refinedoil.

7. In a method as defined in claim 5, wherein the fracturing fluidcontains a propping agent.

8. In a method as defined in claim 7, wherein the propping agent issand.

2. In a method as defined in claim 1, initially fracturing saidformation by a fracturing fluid containing a propping agent, andthereafter injecting said composition into the fissures formed by saidfracturing fluid.
 3. In a method as defined in claim 1, wherein saidfracturing occurs in a soft calcareous formation.
 4. In a method asdefined in claim 1, wherein said oil is a Member selected from the groupconsisting of kerosene, diesel oil and refined oil.
 5. A method ofpreventing the closure of fissures in a hydrocarbon bearing undergroundfractured soft calcareous formation to permit the production ofhydrocarbons from said formation, which comprises injecting a hydraulicfracturing fluid down a bore hole communicating with said formation at apressure sufficient to form fissures therein, injecting into said formedfissures a treating composition consisting essentially of cement, fromfour to eight parts by weight of 20-40 mesh size sand, from 0.4 to 0.8part by weight of a hydrocarbon oil, from 0.01 to 0.10 part by weight ofa oil wetting agent, and 0.02 to 0.04 part by weight of finely dividedsilica of 200-325 mesh size, each per part by weight of cement, saidcomposition being suspended in an aqueous carrier medium in an amount offrom about 1 to 10 pounds per gallon of said carrier medium, contactingsaid injected treating composition in said fissures with an aqueoussolution of a water soluble surface active agent to water wet the cementcomponent thereof, maintaining pressure on said composition for apredetermined period to permit the formation of a fluid permeable cementbarrier in said formed fissures, where said hydrocarbons in saidformation can be recovered through said formed permeable cement barrier.6. In a method as defined in claim 5, wherein said oil is a memberselected from the group consisting of kerosene, diesel oil and refinedoil.
 7. In a method as defined in claim 5, wherein the fracturing fluidcontains a propping agent.
 8. In a method as defined in claim 7, whereinthe propping agent is sand.